Tanning compositions and their manufacture



Patented Feb. 26, 1946 I 2,395,472

. 2,395,472 TANNING COMPOSITIONS AND THEIR I MANUFACTURE Herbert B. Fernald, Cleveland, and Ralph K. ller, Cleveland Heights, Ohio, asslgnors to E. 1. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application February 25, 1942, Serial No. 432,256

1 claim. (01. 8-94.19) This invention relates to compositions adapted agents as are desired to adapt the composition to to be dissolved in acid to produce silicic acid soluits intended purpose. For instance, dissolving a tlons suitable, among other things, for use as sodium aluminum silicate in a dilute acid'causes tanning baths. The invention is more particuthe formation of a silicic acid sol and an alumilarly directed to compositions comprising ahydronum salt of the-acid. If the sodium aluminum gen bonding donor compound and an acid-solusilicate is dissolved in the presence of a hydrogen ble, double silicate of an alkali metal and a metal bonding agent one immediately obtains a tanning selected from the group consisting of aluminum, solution. The tanning solution can therefore be chromium, iron, zinc, titanium, and zirconium, prepared simply by dissolving the compositions of the composition dissolving in acid to form modl- 10 this invention in a dilute acid and workmen are lied silicic acid sols useful for such things as tancalled upon to efiect no chemical control other ning, insolubilizing protein, and strengthening than that on acidity with which they are already paper. The invention is also directed to a preentirely familiar because of the frequent pH adcipitated sodium aluminum silicate and to procjustments in normal tanning processes. Simiesses for its manufacture. larly, compositions may be made up with double Practices for tanning skins with silicic acid silicates using instead of aluminum a metal such have recently been improved by the inclusion of as chromium, iron, zinc, titanium, or zirconium a hydrogen bonding agent in the tannage. These and corresponding tanning solutions can be prenewly-improved baths customarily contain a pared simply by dissolving the double silicate in a silicic acid sol, a hydrogen bonding agent, and suitable acid.

aluminum sulfate, and tanners find considerable Double silicates used according to the present difiiclllty in accurately proportioning the mateinvention will ordinarily have an alkali metal as rials needed at the place of use. Many tanners one ti d an amphoteric, tanning metal are poorly equ pp d u a accurately to as a second cation. The alkali metal cation may measure out the reactants and to carry out the be lithium, Sodium, or potassium, The s ond procedure f r pa in t e rather complicated cation should be selected from the group consisttanning solution. Most tanners prefer a composlmg f aluminum chromium, iron, zmc, titanium, which can be dlssolved and made ready and zirconium since compounds of these metals for use by workmen cmwmiively unskmed in are valuable modifying agents in silicic acid tanthe manufacture of chemicals.

nin solutions.

Any double silicate of the type described may be used which is acid-soluble. There may be used, for instance, any of the natural silicates occurring in nature. Suitable naturally occurring sodium aluminum silicates, for instance, are anal- It is an object of this invention to provide prepared compositions which can be dissolved in an acidulous medium to produce tanning compositions comprising silicic acid sols and suitable aluminum compounds, or other metal compounds, s?gfiglfigi? i gfigfggfi gigg i fi cite, naturolite, and nethelite. Natural sodium prising an acid-soluble, double silicate of an alkali alummum and other 9 smcates Wm metal and a metal Selected from the group com frequently contain insoluble material and will fresisting of aluminum chromium, iron zinc, quently be made up of mixtures of silicates, but ta and z1rconium together with modifying these are all suitable so long as they form silicic agents adapting t product to the uses for which acid sols admixed with an aluminum salt or other it is intended. is a further object to provide suitable metal salt upon being dissolved in a dilute compositions comprising sodium aluminum siliacldcate with modifying agents particularly ti Instead of these naturally occurring silicates the product to its intended purposes. It is a still thcrc y e d a o e slmllcr co pou s further object to provide a precipitated, acidpar d mm ial y. Typ f these c msoluble sodiumaluminum silicate and to provide Pounds are Sodium aluminum silicates p p simple and economical processes for its producfor instance. y a t n a s a wi n u tion. Further objects will become apparent herenum compound, Examples of such materials will inafter. i be found in the Benson Patent 2,244,383 and in Compositions of this. invention are generally the Schorger Patent 1,949,360. Sodium aluminum characterized by containing an acid-soluble, silicates are also produced by heating kaolin with double silicate together with a hydrogen bonding a sodium hydroxide solution. Other double siliagent and with or without such other modifying cates may be produced by analogous reactions.

While double silicates and particularly sodium aluminum silicates occurring in nature or prepared as are the synthetic zeolites may advantageously be used, the preferred practice of the present invention is to use a water-insoluble, acidsoluble, precipitated double silicate and particulariy a precipitated sodium aluminum silicate particularly described hereinafter.

Aluminum silicate compositions of the present invention ought to have a mol ratio of AlzOstSiO:

of 1:2 to 1 :5. For tanning it is preferred that the ratio be between 1:2 and 1:4. Natural sodium aluminum silicates selected or artificial materials prepared ought to have an AlaOaZSiOa ratio within the limits. It will be understood, however, that if a natural or prepared sodium aluminum silicate might be designated as weak'organie bases fore describe the agents added to silicic acid sols which is made at a high pH by processes more has a ratio difierent from that which'is desired,

for instance in a tanning composition, this can be adjusted at least to some extent by adding an aluminum compound such as alum to increase the A1203 content. In the case of prepared sodium aluminum silicate it will ordinarily be desirable to predetermine the ratio and mixtures may be made with natural materials to produce a product having substantially any desired ratio for tanning. Similarly with compositions using metals other than aluminum, the metal ought to be present in a ratio metal oxide:SiOz about as indicated for aluminum.

Tanning compositions according to the present invention include a hydrogen bonding donor compound. Hydrogen} bonding is a concept advanced inrecent years to explain certain abnormalities in the chemical and physical behavior of mixtures other an atom capable of donating a pair of electrons to form a directional or eta-ordination bond.

Since the bond is formed by the donation of anelectron pa r from one atom, the donor to the other atom he bond is not of the type conceived as an ordinary valence bond but many of the properties of the mixture indicate that a type of chemical compound is formed. These mixtures,

for instance, exhibit an abnormal vapor pressure lowering, that is abnormal deviation from Raoults law. There is further observed abnormal heats of mixing and abnormal deviation in viscosl-ty and freezing point lowering.

When silicic acid is mixed with an organic hydrogen bonding donor compound it exhibits characteristics unexplainable upon the basis of ordinary chemical reaction and unexpected from a consideration of the characteristics of the materials mixed. Apparently silicic acid has an acceptor hydrogen atom and forms some type of compound with a hydrogen bonding donor.

' Among the characteristics of these silicic acidhydrogen bonding donor combinations is a decreased tendenc to precipitate gelatin and an increase in the time required for the sol to be converted to the gel.

It will be understood that in advancing the theory of hydrogen bonding it is not intended to limit or restrict the. present invention, the explanation being given only for purposes of illustration. Whatever the reason the type or compounds known to be organic hydrogen bonding donors profoundly modify silicic acid sols and may desirably be included in the compositions of the I present invention.

It will be seen that hydrogenbonding donor compounds are of the type of materials which according to the present invention as water-soluble, organic bases which will not raise the pH of silicic acid above 7. It is again observed that while the terminology of either the hydrogen bonding theory orthe weak base theory may advantageously be used in describing the present.

invention to those skilledin the art in commonly understood language applicants do not consider the adoption of either theory as bearing upon the invention save as it gives a convenient system of terminology. v

While any hydrogen bonding donor compound. (or weak base) may be used with silicic acid according to the present invention it will generally be found desirable to use any water-soluble hy-.

drogen bonding donor compound selected from the group consisting of ethers, amides, alcohols, ketones, and esters of phosphoric acid.

Hydrogen bonding donor compounds used in the compositions of this invention should be water-soluble at least to the slight extent required .to permit formation of a coordination complex alcohols, ketones, and esters of phosphoric acid. It is preferred that the ethers have an oxygen or nitrogen atom in addition to that in the ether linkage and specifically it is desirable that the ether contain in addition to the ether group a second ether group, a hydroxy group, an amide group, or an ester group. In the ethers the two carbon atoms attached to the oxygen. atom of the ether linkage should not be attached to each other. Amides for use with silicic acid sols according to the present invention are preferably N-substituted. Alcohols for use as donors ought to contain more than two carbon atoms. Alcohols are among the weakest of the hydrogen bonding agents but may find value in some instances, Ketones are not quite as weak as alcohols and any water-soluble ketones may be used as above discussed. Esters of phosphoric acid are quite efiective hydrogen bonding agents and may frequently be included in compositions-of this invention to advantage. 7

-Ethers are among the preferred hydrogen a bonding donor compounds for inclusion in compositions according to the present invention. In

addition. to containing an ether group these KAC': cording to this theory the materials involved act ed from the group consisting of ethers, amides,

Polyethylene glycol adipate Dlethyl ether of diethylene glycol Dloxane Dioxolane Dlethyl ether or ethylene glyc Dimethyl ether of ethylene glycol Triethylene glycol dipropionate Glycerol formal Ethylene glycol acetal Sorbitol triacetal N,N-Dimethylmethoxyacetamide N-Acetylmorpholine N,N-Adipyldlmorphollne Dlmorpholide urea Polyethylene oxide Monomethyl ether of ethylene glycol-ethylene oxide reaction product Ethylene glycol-ethylene oxide reaction product Glycerol-ethylene oxide reaction product Ethanolformamide ethylene 'oxide reaction a product Amides are among the preferred hydrogen bonding donors for use in compositions according to this invention. Whereas oxygen is the donor atom in others the nitrogen of amides probably acts as the donor atoms. Among the most eflective compounds of this group are the N- substituted amides and the di-substituted com.. pounds are preferred. It will be seen that some of the compounds in the above list or ether's are amides as well and could have been shown below as illustrative of the use of amides.

Examples oiamides are listed below, ureas. and other amides being listed separately:

Ureas Tetramethylurea Tetraethylurea Urea Thiourea N,l l'-Diethyl-N,N'-diethanolurea Nonaethylene glycol N,N'-Diethanolsuccinamlde Dimethyl ether or tetraethylene glycol N-Formylhexamethylenlmlne Dimethyl ether or diethylene glycol Diethylcyanamide Hexaethylene glycol Acetamide Butyl ether of diethylene glycol 5 Succinamide Ethyl ether of diethylene glycol acetate Formamide gii fifi fii g i g glycol Examples of Ketones may be given as follows: Monoethyl ether or diethylene glycol Ketones: Trlethylene glycol i0 Acetonylacetone Monoethyl ether of ethylene glycol Acetone Monomethyl ether of ethylene glycol Formacetoethyl methylene glycol Methyl acetoacetate NN' -Bisweta-methoxyethyl) adlpamide V Diacetone alcohol N,N-Bis(methoxymethyll urea 15 Examples of Alcohols may be given as follows:

Alcohols:

Diacetone alcohol Z-Methyl-ZA-pentanediol Isopropanol Pinacol Hexamethylene glycol Pentaglycol Tert-Butyl alcohol Tetrahydroxy octane 1,1,1-Trlmethy1o1ethane Propanediol Esters of phosphoric acid: Tributyl phosphate Triethyl phosphate Tri-isopropyl phosphate Tri-isoamyl phosphate Hexyl phosphate Tri(butyl ether of diethylene glycol) phosphate The amount of hydrogen bonder to use in a particular composition varies considerably with the results desired and with the particular double silicate and the particular tanning procedure to be followed. The amount of donor should of.

course not be so great as to slow the tanning unduly and yet it should be suflicient toprevent too rapid a tanning. The precise amount of a particular agent to use in a particular instance can best be determined by making up a few sample compositionsand then trying tanning baths made with them. In general it may be indicated that there should be used an amount of donor ,such that when a tanning solution has been made up with the composition the donor will be equivalent to from about 0.1 per cent to about 10 course be used in accordance with the customary v practice since too much of the masking agent will too greatly retard tanning. In general from about 5 per cent to per cent of the weight of alumina, or other metal as oxide, may be used.

Compositions according to the present invention may contain still other modifying agents and there may be included, for instance, other tanning agents and tanning assistants. The compositions of the present invention may adacids.

vantageously be used for insolubilizing protein, for strengthening paper, and for numerous other purposes and suitable modifying agents may advantageously be added depending upon the specific use for which the compositions are intended.

In making up tanning solutions with the compositions of the present invention it is only necessary to dissolve the composition in a dilute acid.

Ordinarily dilute sulfuric acid sumcient to bring I Alternatively there may be employed such a final pH of about 1.5 to 3.5. Still more speciiically, it will be preferable to reduce the pH to about 2 to 3. Itwill be understood that while any acidulous material may be used to increase the acidity of silicate solutions to produce silica sols, some acidulous materials do not themselves have a low enough pH to produce the final acidity desired. In this event such an acidulous material may be used in combination with a more acidulous material, and as will be evident mixtures of two or more acidulous materials may be used as seems desirable.

. Acids maybe included in compositions of the present invention by mixing the compositions with such dry acids and acidulous materials as sulfamic acid and sodium acid sulfate. To minimize the reaction between the solid acid and the double silicate one or both the ingredients can be coated with an inert prior to mixing. If the compositions are to be stored any length of time there'is unfortunately a tendency to premature reaction and it will ordinarily be found desirable under these circumstances to offer the components separatelyor else simply as indicated above to let the tanner add the composition to a dilute acid solution.

The concentration of tanning agents made'up using compositions of the present invention may be considerably varied as in prior processes using similar sols. The concentration will depend spepickled. The skins may if desired be depiekled. They may also be given a salt liquor treatment to soften them and to put them in a more uniform condition as is the practice in prior art v tanning processes.

While skins prepared in any manner may be treated using tanning' solutions made up with compositions of this invention, the pH of the skins is important. As will be observed below, the tanning is eifected at certain conditions of acidity and the skins may tend to change these conditions. The tanning solution may suitably be controlled to compensate for variance'of the pH of the skins from that of the taming solution. It may sometimes be found advantageous to adapt the processes for preparing the skins so that a skin prepared for tanning is apprommately at the pH of the tanning solution.

Too rapid reaction of the tanning agent with Y the skins in the first stages of the process should be avoided in order to prevent surface hardenin of the skin. The amount of hydrogen bondin donor used should, as indicated above, be such as to assistin preventing too rapid a tanning and the initial pH of the solution should not be too high. The initial pH of the solution will ordi= narily be from about 1.5 to 3.0. More specifically, it will be found preferable to use a pH of about 2.5. If the initial pH is much above 3.5 the tanning will proceed too rapidly in the initial stages though it will be understood that the pH to be selected in any particular instance will depend upon the specific conditions of the tannage. If

ciflcally upon numerous factors in, the tanning process itself, but it will rarely be found desirable to have an SiOz content greatly in excess of about 2 per cent.

The taming compositions of this invention may be used to make up tanning baths for the treat-.- ment ofany type of skin adapted to be converted into leather or fur. It is-to be observed that the term skin is used generically to include heavy skins such as cowhide, lighter skins such as goatskin and calfskin, and also skins of furbearing It will naturally be necessary to adapt the processes to the type of skin to be treated. For instance, goatskin may be more rapidly tanned than calfskin, but those skilled in the art are well aware of such factors and may readily adapt the compositions of this in=. I vention t'o the specific needs ofparticular specialized problems.

too low a pH is used combination of silica with the skin is too slow and, additionally, excessive acidity may deleteriously afiect the skin. a

' After satisfactory penetration has been obtained the pH of the solution is raised by the addition of any suitable alkali. Raising the pH accelerates the tanning action. The pH should at this'point be raised to about 3.5 to 4.5. Sodium carbonate or other alkali metal or ammonium hydroxides or carbonates or organic bases such as ethanolamines may be used to raise the pH. g

The considerations as to the type of -apparatus to use, the time to be allowed for tanning, the

temperatures of tanning, and the amounts of tanning agent are substantially those known to the art in connection with prior art tanning processes. The time allowed for'tanning must be sufficient to permit complete penetration of the tanning agent, and the pH should not be raised too rapidly or there may be puckering and apparent over-tannage of the grain surface. The tanning can best be effected at room temperature, say 20 to 30 C.

The exact amount of the tanning solution to usecan best be determined by a few simple tests under the specific conditions of the process se- Skins to be tanned employing compositions of i this invention may be prepared in any of the manners customary to the art. They may suitably be unhaired, limed, delimed, and bated and lected and with the specific skin to be treated. In general, enough of the tanning agent must be used to effect the-tanning desired but unduly large amounts should not be used as they will not be taken up by the leather in a reasonable period of time and they may cause overtannage.

. While compositions of the invention may be made as described with various natural and manufactured double silicates, it is preferred to use a reeipitated sodium aluminum silicate, or other double silicate, the manufacture of which will now he described. The precipitated sodium aluminum silicates are acid-soluble, amorphous, soft, chalky, white, and opaque. The ratio AhOaZSiO-z may vary from about 1:2 to 1:5 though the preferred product has a ratio between about silicates are made at a high pH and contain less than 1.5 mole of Nazi) per mol of A1203.

In the preparation of the precipitated silicates oi the invention it will ordinarily be found desirable'to use sodium silicate for the reaction, but it will be understood that any silicate more soluble than its products of reaction with the aluminum compound, or other metal compound, may be used. There maybe used, for instance, potassium or lithium silicates. The SiO'a/NaaO ratio ought .not be substantially greater than 2. It

is preferred to use sodium metasilicate but if a silicate with a higher SiOa/NazO ratio is used an alkali will need to be added. In any event the total in the reaction should be suficlent to maintain a pH of 9 or more. 7

If an alkali is required then any alkali may be used which will bring the pH of the reaction to at least 9, though of course the alkali should not be one which will react with the silicate or aluminum compound to form insoluble by-products.

w As examples of suitable alkalies there may be aluminate, aluminum nitrate, or aluminum chloride. When an aluminum compound such as sodium aluminate! is used it will of course be easier to maintainia pH of QM more during the reaction. 1

It will be found a comparatively imple matter to adjust the composition of the precipitated sodi- 1:8 a; 1:4." The precipitated sodium aluminum 9 or above then the pH may be reduced towards the end of the reaction period to as low as 7 or um aluminum silicate since almost all, say over 90 per cent, of the silica. and alumina used in the reaction will be found in the product. The proportions of reactants should be so selected that the AlzOazSiO: ratio will fall within the limits from about 1:2 to 1:5. Preferably the product will have an AlsOaZSiOa ratio of from about 1:3 to 1:4. Products within these ratios will be found soluble in a 0.1 normal hydrochloric acid solution.

The alkalinityo'f the product should be kept down, and the product should contain not more than 1.5 mols of NazO per mole of A1203. The

use of large excesses of alkali in the reaction should therefore be avoided and the produc should be carefully washed. To effect reaction the soluble silicate and the soluble aluminum compounds are each first put in solution and then these olutions are brought together. The solution of silicate may'ordinarily contain from about 5 to 15 per cent of solids and the solution of the aluminum compound may similarly contain about 5 to 15 per cent solids. The final mixture should not contain much in excess of about 20 to 25 per cent solids by weight.

It will be understood that in effecting reaction it will ordinarily be found desirable to add the 8 without markedly injuring the product. It

' may frequently be found desirable after the remay be filtered and washed. The product can be made more easily filterable by eflfecting the reaction at superatmospheric pressures or at elevated temperatures or both. Ordinarily, however, no substantial benefit is derived from the use of either heat or pressure.

While the precipitated sodium aluminum sillcate of this invention is'particularly well adapted for use in tanning compositions in conjunction with a hydrogen'bonding agent it will be appar ent that the product may find numerous other uses. The product is soft, chalky, pulverulent, and extremely reactive. The product is suitable for use as a filler in rubber and plastics and may be used as a substitute for or in conjunction with clay as a paper filler and in compositions for paper coating. The product may also be used as a base exchange medium. as a carrier for pesticides, as an ingredient in cement, as a catalyst or catalyst carrier, and as a pigment base for instance by adsorbing dyes on the sodium aluminumsilicate.

While the above discussion illustrating the preparation of a precipitated sodium. aluminum silicate has been directed to a particular double silicate, it will be understood that the principles shown are applicable to the formation of various double silicates using any alkali metal and any metal selected from the group consisting of aluminum, chromium iron, zinc, titanium, and zirconium. For the preparation of other such acidsoluble double silicates the reaction conditions will be similar and the proportions and ratios of reactants will similarly be selected to produce compounds suitable for use in tanning or varioils of the other uses as outlined above.

In order that the invention may be better understood reference should be had to the following illustrative examples:

Example I A precipitated sodium aluminum silicate was prepared according to a process of the invention as follows:

Twenty-four and nine-tenths parts by weight of commercial iron-free aluminum sulfate (containing 16 per cent A1201) dissolved in 132 parts by weight of water was slowly added with vigorous agitation to a solution containing 31.5 parts by weight of a sodium silicatesolution containing Naz0=9.1 per cent and Si02=29.7 per cent and 10.0 parts by weight of flake caustic (equivalent to 6.85 parts of Nero) dissolved in 1'75 parts by weight of water. The SiOzzNazO ratio by weight of the final silicate solution used was 0.96. The

additional sodium hydroxide was used therefore to adjust the alkalinity to that required tomaintain a pH of about 9 during the reaction.

The aluminum sulfate was added directly into the vortex of a stirrer so as to have rapid and efficient mixing.

After all the aluminum sulfate had been added,

the reaction slurry was stirred for-.15 minutes toinsure complete reaction. This slurry contained 18.5 parts of sodium aluminum silicate and 16 parts of sodium sulfate in approximately 330 parts by weight of water. Throughout the reignition. S102 :AlaOs=4.35 1 and action the pH was above 9 and at the end of the reaction was about 10.5.

The product was filtered out, washed to'remove the sodium sulfate and then dried for hours at 110-115 C. 18.0 parts by weight of the dry product was obtained containing 43.20 per cent S102, 22.41 per cent A1303, 17.2% per cent NaaO and 17.70 per cent ignition loss. The yield was 97.2 per cent of the theoretical. This particular product had a ratio of .8192 to AlrOs of 3.23 to 1, and a ratio of NaaO to A1203 of 1.26:1.

From the composition of the material it was found that all the aluminum and 87-88 per cent or the silicate used in the reaction appear in the final product.

for the various uses indicated above. It was particularly excellent when used in tanning compositions of the invention. Examples of tanning com- T (16.0 per cent A1203) was dissolved in 80.0 parts pofitions using precipitated aluminum silicates Y are given hereinafter.

Example I! Since the ratio between Nazo and S10: is 1:1 in sodium metasilicate, it can be used instead of the sodium silicate and free alkali used in Example I in the production of precipitated sodium alu- A1203). dissolved in 180 parts 'by weight 0! H2O,

wasreacted with 83.16 parts by weight of sodium metasilicate (28.62 per cent S102) dissolved in 400 parts by weight of water. This reaction was carried out in the same way as outlined in Example I. The ratio of $102 to A1203=5.'74 in the reaction mixture. At no time during the reaction did the pH go substantially below about 9.

The precipitate was filtered out, washed and dried. The material thus obtained was white, chalky, amorphous, easily pulverized, and very soluble in dilute acids. Analysis showed it to contain 19.03 per cent A1203, 15.45 per cent NazO,

48.90 per cent S10; and 15.25 per cent loss on Nac0:Al-.-Oa=1.33:1

in the final product.

Example III,

The acid-soluble, precipitated sodium aluminum silicate of the invention can convenientlybe prepared using sodium aluminate as the source of aluminum. Products were prepared vby'procedures similar to those of the previous examples but reacting a solution of sodium aluminate with sodium metasilicate solution. The sodium alufate with caustic soda and the reaction product thus prepared was then reacted with sodium metasilicate solution. During the reaction with sodium metasilicate the pH did not drop below The products produced were white,

sodium metasilicate as in this example had Na2O:A12O3 ratios of about 1.0 to 1.4.

Example IV Sixteen and twenty-five hundredths parts by weight of commercial iron-free aluminum sulfate by weight of water. Concentrated caustic solution was added to this solution until the precipitate which first formed redissolved.

This solution is then added with violent agitation to a solution containing 10.48 parts by weight of sodium metasilicate, 75 parts by weight 01 water. The SiO2:A12Oa was 2:1 in this'reaction mixture.

The precipitate which formed was filtered. washed and dried. Awhite, porous, easily pulverized material was obtained. This material was rather dimcultly soluble in acid solution.

By analysis this material contained 33.85 per cent SiOz, 29.78 per cent A1203, 18.25 per cent 119.20, and 12.68 per cent less on ignition. $192 to A120: ratio in the product=2.21 to 1. A120a=1.01 to 1. The pH throughout the reactiOn was maintained above 11.

Example V Twenty and five-tenths parts by weight of sodium aluminate (NaaAhOO dissolved in 240 parts by weight of water was added with stirring to a solution containing 101 parts by weight of a sodium silicate solution (Naz0=9.1 per cent, SiOz =29.7 per cent) and 222 parts by weight of sodium hydroxide dissolved in 1120 parts by weight Example VI A tanning composition of the present invention was made up using precipitated sodium aluminum silicate prepared as in Example I. 27.5 parts by weight of the precipitated aluminum silicate was mixed with 11.2 parts by weight of urea. 35.5

parts by weight of suliamic acid was dissolved in 200 parts by weight of water and the preparedcomposition was then readily dissolved in the water. 100 parts by weight of drained 'goatskin which had been prepared in the usual way by unhairing, deliming, and pickling were put into this minate was prepared by reacting aluminum sulsolution in atanning drum and thoroughly mixed. The skins were agitated for one hou and then the addition of a 10 per cent solution of sodium acetate was begun. By repeated additions of sodium acetate over a course of 7.5 hours, the pH of the solution was brought to a final valueoi pH 4.0. The solution was then drained from the drum. The tannedskins were piled down over night. The next morning they were neutralized to a pH of 5.5 with 10 per cent sodium bicarbonate solution during 1%; hours with further agitation. Subsequently the hides were washed with water and fatliquored with a sulionated oilfneat's-foot oil mixture. The tanned skins were soft, pliable, white, and had a shrink temperature of about to F.

A similar. composition was made up in which the dry sulfamic acid was admixed with the pre-.

cipitated aluminum silicate and urea. This mixture was fairly stable and for use it needed only to be added to a correct amount of water.

Example VII .Fifty parts of pulverized precipitated sodium NazO to terial, but due to the extreme porosity and absorbent nature of the precipitated sodium aluminum silicate, the liquid nonaethylene glycol is completely absorbed, the mixture appearing to be a dry powder. The tanning composition thus prepared can be dissolved in an acid solution for use in tanning as in Example VI.

Example VIII Fifty parts of precipitated sodium aluminum silicate are mixed with 21.8 parts of tributyl phosphate. As in the previous example, although the tributyl phosphate is a liquid, the resulting mixture is an apparently dry light powder. The tanning composition may be used as in Example VI by dissolving it in a dilute acid.

. Example IX Fifty parts by weight of sodium aluminum silicate prepared as in Example I were mixed with 25 parts of powdered urea. To this mixture was also added 25 parts by weight of sodium acetate which had previously been pulverized to pass a 100 mesh screen. The mixture was agitated until the ingredients were thoroughly in-- termingled. Upondissolving this composition in dilute sulfuric acid a tanning solution is produced containing silicic acid, a hydrogen bonding agent, aluminum sulfate and a masking agent.

Example X One hundred one and five-tenths parts of granular sodium acid sulfate in the form of shot of such a size that it will pass thru a screen having 6 meshes to the linear inch but will not pass thru a screen having 30 meshes to the linear inch, are mixed with 41.1 parts of sodium aluminum silicate and 17.7 parts of tributyl phosphate. When One hundred three parts of shotted sodium acid sulfate of the type used in the previous example are mixed with 41.1 parts of precipitated sodium aluminum silicate, 20.0 parts of urea, and 33.0 arts of anhydrous sodium acetate. When this mechanical mixture is dissolved in about 800 parts of water, a solution is obtained suitable for tanning.

In order to prevent segregation of the various ingredients from these mechanical mixtures, it is advantageous to mix them thoroughly and then compress the mixture into pellets or small briquettes which readily disintegrate upon bein agitated with water.

Although the particle size of the ingredients is not important if the mixture is to be used with-- in a few days, it will be found that if all the ingredients are finally pulverized prior to mixins, some interaction between the sodium acid sulfate and the sodium aluminum silicate will take place. In order to minimize this eflect, I prefer to use relatively coarse sodium acid sulfate in the shotted form, since in this state it is much less reactive than when pulverized to mesh.

In order to minimize the reaction between the solid acid and the sodium aluminum silicate, one or both ingredients can be coated with an inert substance prior to mixing, e. g., the sodium bisulfate pellets may be stirred wtih 2 per cent by weight of calcium stearate which coats the pellets with a thin white adherent film, before mixing with the sodium aluminum silicate.

Example XII Fifty parts of laumontite, a naturally occurring calcium sodium aluminum silicate, is ground to pass a screen having 300 meshes to the linear inch and is mixed with 20 parts of powdered urea which had been previously pulverized to pass the 100 mesh screen. The mixing is continued until the ingredients are thoroughly intermingled. The tanning composition may be used as in Example VI, by dissolving it in dilute sulfamic acid solution, using suflficient acid to maintain the mixture at a pH of about 2 until substantially all the acid-soluble material in the mineral is dissolved. Tanning with this solution may then be carried out as in Example VI.

Example XIII Fifty parts of sodium aluminum silicate of the gel-type similar to that described in the Benson Patent 2,244,383 was ground so as to pass a screen showing 300 meshes to the linear inch and was thoroughly mixed with 11.6 parts by weight of carbitol acetate. This tanning composition may be dissolved in sufilcient dilute acid solution so that the pH is maintained at around 2 until all the mixture is dissolved. The gel-like sodium aluminum silicate dissolves at a much slower rate than the precipitated material. The tanning procedure is carried out as described in Example VI.

Tanning compositions similar to those of the example may be made up using hydrogen bonding agents and double silicates of chromium, iron, zinc, titanium, and zirconium.

While we have shown certain illustrative processes and compositions it will be understood that the invention is not to be limited thereby, and while the illustrative examples show the use of the compositions for tanning skins it will be understood that the compositions may be used for insolubilizing protein, strengthening paper, and for any other use.

We claim:

A solid composition, adapted to be dissolved in acid to produce a modified silicic acid sol, comprising an o anic hydrogen bonding donor compound and a precipitated sodium aluminum sili- 

